1. Field of the Invention
The present invention generally relates to an apparatus for coating fine particles to produce a thermal transfer image receiving sheet for use in a thermal transfer recording, a method of producing a thermal transfer image receiving sheet by using the apparatus, and a thermal transfer image receiving sheet produced thereby.
2. Description of the Related Art
In a so-called sublimation type thermal transfer recording, an image is formed on a thermal transfer image receiving material by using a thermal transfer recording medium. The thermal transfer recording medium is composed of a base film and an ink layer formed on the base film. For example, the base film of the thermal transfer recording medium is constructed by a polyethlene terephthalate (PET) film, and an ink layer of the thermal transfer recording medium is constructed by sublimation dye. On the other hand, the thermal transfer image receiving material is formed by a paper, plastic film, etc. More specifically, when a thermal energy supplied to the thermal transfer recording medium by a heating device such as a thermal head, the sublimation dye in the ink layer of the thermal transfer recording medium is diffused and transferred onto the thermal transfer image receiving material. The density gradient of the sublimation dye can be adjusted by a unit of a dot, so that various full color images can be formed on the thermal transfer image receiving material by the sublimation dye.
Here, it is required that the thermal transfer image receiving material has a character to keep the shape of image formed by the sublimation dye diffused and transferred thereon.
In this regard, in the sublimation type thermal transfer recording, an exclusive paper (image receiving sheet) is used. The image receiving sheet is composed of a base film and a dye receptor layer formed on the base film in advance. More specifically, the base film of the image receiving sheet is constructed by a plain paper, a synthetic paper, etc. Further, the dye receptor layer formed on the base film is constructed by resin having a dyeing property, such as vinyl chloride, vinyl acetate, polyester, etc. Namely, the solution of the aforementioned resin is coated on the base film, and the solution coated on the base film is dried. Thus, the continuous coat called the dye receptor layer is formed on the base film.
Further, in order to improve the quality of an image formed on the thermal transfer image receiving sheet, research on the thermal transfer image receiving sheet is doing. Thus, a thermal transfer image receiving sheet having a dye receptor layer constructed by at least two regions of micro phase separation resins, whose dyeing properties are different from each other, has produced. More specifically, when the dye receptor layer is produced, a resin is separated into two parts having the same components each other, and one part is sensitized and other part is untreated, and then, the two part are mixed. Then, this mixture solution is coated on the base film. On the other hand, the dye receptor layer is also produced another method mentioned below. Namely, one resin having a high dyeing property and another resin having a low dyeing property, which are not compatible each other, are mixed each other. Then, this mixture solution is coated on the base film.
However, in the aforementioned thermal transfer image receiving sheet having a dye receptor layer constructed by two regions of micro phase separation resins, the resins included in the dye receptor are amorphous. Therefore, it is difficult to control their size, arrangement or shape. Namely, in the aforementioned thermal transfer image receiving sheet having a dye receptor layer constructed by two regions of micro phase separation resins, the distribution of the resin having a high dyeing property and the resin having a low dyeing property cannot be controlled. Therefore, nonuniformity is formed in the direction of plane and depth, so that the quality of an image becomes ununiform. The size of each of the resin having a high dyeing property and the resin having a low dyeing property is fixed by the kind of resin used therein or the condition of the solution. Therefore, the size of the network in the network structure in the dye receptor layer cannot voluntarily controlled, so that there are much restriction when the dye receptor layer is designed, and thus, the design of the dye receptor layer is difficult. Further, the boundary between the resin having a high dyeing property and the resin having a low dyeing property is not clear. Therefore, the dyed portion has continuity in a macro angle, so that dye is bled at the edge of print, and thus, the edge of the print is indefinite.
Further, in the sublimation type thermal transfer recording, since an image is recorded by thermal diffusion, the boundary between a record part and a blank (not record) part is indefinite because of the concentration gradient between these parts.
On the other hand, in the thermal transfer recording using a melting type ink film, ink is not fixed on the dye receptor layer, so that an image cannot printed. Therefore, this kind of the thermal transfer image receiving sheet cannot used with the melting type ink film.